1. Field of the Invention
This invention relates to the field of so called non pneumatic tires. More particularly ,this invention relates to a class of wheels involving outer and inner rings and a space between them where some flexing structures are provided. The said flexing structures being in form of web-like objects able to flex under in the load and providing an equivalent of the pneumatic tire behaviour.
This class of wheels including the "non-pneumatic" term was started by pioneers like Long at Goodyear in the late seventies and Palinkas,Hybakken,Ims,Pajtas at Uniroyal in late eighties and is believed to play a significant role in the future of wheel technology. All these pioneers dedicated their life to the rubber and polyurethane wheel applications and Horst Ims worked at Pennemunde as a mechanical engineer later specializing in polymer technology.
2. Prior Art
The prior art is described in the Long&Rye Palinkas,Hybakken ,Pajtas patents and essentially is based on a central web in the form of a ring/disk placed symmetrically in the space between the outer and inner annular rings of the wheel. Essentially this disk is the main load carrying object of the wheel.
The concept of two annular rings with a space between them making the basic structure of the wheel was probably first time presented by Long and Rye in U.S. Pat. No. 4,226,273. The space between the said rings was occupied by some flexing structures anticipating the later work of Palinkas and all.
Coming back to the closest prior art (Palinkas and all) this load carrying ring/disk is reinforced or supported laterally on each side by inclined webs so that when the load is applied they can flex thereby simulating the effect of a pneumatic tire.
When rolling the structure formed of the central web and the lateral webs are flexing under load . The central web has a buckling type of flexing and the lateral webs simply bend.
The tests proved in time that the stress spectra generated in the central and lateral web structure has peaks in the area connecting the central disk with the inner surface of the outer annular ring (the rim) of the wheel.
The cyclic nature of the stress combined with the magnitude of it generated a combined effect of either heat or fatigue or a combination of these depending on the load and the time the wheel was used.
Even at normal loads--in the case of spare tire application--after a certain number of cycles the area where the central disk is united with the rim overheated reaching temperatures in excess of 120 to 150 degrees Celsius. The material melted and affected the area between the rolling rim and the web structure ending in failure of the wheel.A combination of hysteresis and low heat dissipation capability inherent to polymers created the failure conditions. In the case of polyurethane this was even more dangerous because the polyurethane melts when it reaches a certain temperature.
This initial class of non pneumatic tires had a lot of hope to use the flexing effect and to eliminate the hysteresis melting typical for the solid tires. In that case the only wear expected from the tire was supposed to be the outer lining involved directly in the rolling contact-which was a wear based on abrasion mainly, Velcro effect and flakes generated by Hertz/Palmgren effect. However this did not happen, the stumbling block being the generation of the hot areas which produced the failure of the wheel.
The heating effect was also generated by the fact that, the outer rim was softer than the web flexing/supporting structure so the deformation and the shearing and compression stress structure was different for the two materials, resulting in stressing the bonding area and also the structural connection between the central disk/web and the annular outer element.
It is an object of this invention to provide a flexing supporting structure between the inner and outer rings of the non pneumatic tire to reduce the stress and heat generated by hysteresis so that the wheel to be used safely in high speed and safety applications-the only wear expected being the one associated strictly with the outside surface of the wheel,.
It is yet a further object of this invention to provide a wheel with increased load capacity.
It is a still further object of this invention to provide a wheel easier to manufacture than those in the prior art.